A radiation barrier is a type of building product that reflects thermal radiation and reduces heat transfer. Because heat energy is also transferred through conduction and convection, the radiation barriers are often equipped with thermal insulation products that slow down heat transfers through conduction or convection.
The Radiant barrier reflects heat radiation (heat radiation), preventing transfer from one side to the other due to reflective surface, low transmit power. In building applications, these surfaces are usually very thin, such as aluminum foil. Foils can be coated for resistance to elements or for abrasion resistance. The luminous barrier may be one or two sides. A side beam barrier may be attached to insulating material, such as polyisocyanate, rigid foam, bubble insulation, or OSB. In addition, the reflective band can be fitted with a radiation barrier strip to make it a adjacent vapor barrier, alternatively, a radiation barrier can be perforated for steam transmission.
Video Radiant barrier
Reflection power and emissivity
All materials emit, or emit, energy by thermal radiation as a result of their temperature. The amount of energy emitted depends on the surface temperature and the property called emissivity (also called "emittance"). Emissivity is expressed as a number between zero (0) and one (1) at certain wavelengths. The higher the emissivity, the greater the radiation emitted at that wavelength. The property of the related material is reflectivity (also called "reflectance"). This is a measure of how much energy is reflected by the material at certain wavelengths. Reflectivity is also expressed as a number between 0 and 1 (or percentage between 0 and 100). At a wavelength and incidence angle, the emissivity and reflectivity values ​​are 1 by Kirchhoff law.
Radiation barrier materials should have low emissivity (typically 0.1 or less) at the wavelength at which they are expected to function. For typical building materials, the wavelength is in the medium and long infrared spectrum, in the range of 3-15 micrometers.
Radiation barriers may or may not show high visual reflectivity. While reflectivity and emissivity should amount to 1 at certain wavelengths, the reflectivity at a set of wavelengths (visible) and emissivity at a set of different (thermal) wavelengths does not always amount to 1. Therefore, it is possible to create dark-looking colors surface with low thermal emissivity.
To do it properly, the radiation barrier needs to face the open space (eg, air or vacuum) through which there will be radiation.
Maps Radiant barrier
History
In 1860, French scientist Jean Claude Eugene Peclet experimented with the insulating effects of high and low emissive metals facing the air space. Peclet experimented with various types of metal from tin to cast iron, and came to the conclusion that both color and visual reflection were significant determinants of material performance. Peclet counts the reduction of BTUs for high and low emissive surfaces facing various air spaces, discovering the benefits of a radiation barrier in reducing heat transfer.
In 1925, two German businessmen Schmidt and Dykerhoff filed a patent on a reflective surface for use as a building insulation because the latest improvements in technology enabled commercially low emissivity aluminum foil. This became the launch pad for radiation barriers and reflective insulation around the world, and within the next 15 years, millions of square meters of radiation barriers were installed in the US alone. Within 30 years, the shining barrier made a name for itself, and was included in a project at MIT, Princeton, and Frank Sinatra's residence in Palm Springs, California.
Apps
Space exploration
For the Apollo program, NASA helped develop thin aluminum foil that reflects 95% of radiant heat. Metalized films are used to protect spacecraft, equipment, and astronauts from thermal radiation or to retain heat in extreme room temperature fluctuations. The aluminum was vacuum-coated onto a thin film and applied to the base of the Apollo landing vehicle. It is also used in many other NASA projects such as James Webb Space Telescope and Skylab. In a vacuum where temperatures can range from 250 ° F above up to 400 ° F below zero, heat transfer is only by radiation, so the radiation barrier is much more effective than on earth, where 5% to 45% heat transfer can still occur through convection and conduction, even when effective radiation barriers are deployed. The Radiant Barrier is Space Foundation Certified Space Technology (TM). The Radiant Barrier was inducted into the Space Technology Hall of Fame in 1996.
Textile
Since the 1970s, metalized polyester sheets called blankets have been commercially available as a means of preventing hypothermia and other cold weather injuries. Due to its durability and light weight, these blankets are popular for survival and first aid applications. The crowd can be seen in metalized reflective films after a marathon, especially where temperatures are very cold, such as during the ING New York City annual marathon that takes place in the fall.
Window maintenance
Windows glass can be coated to achieve low emissivity or "low-e". Some windows use a laminated polyester film in which at least one layer has been metalized using a process called sputtering. Sputtering occurs when a metal, most often aluminum, is evaporated and a polyester film is passed through it. This process can be adjusted to control the amount of metal that ultimately coats the surface of the film.
These metalized films are applied to one or more glass surfaces to withstand the radiation heat transfer, but the films are so thin as to allow visible light to pass through. Because the thin films are brittle and can be damaged when exposed to air and moisture, manufacturers usually use many pane windows. While films are usually applied to glass during manufacture, some films may be available for homeowners to apply for themselves. Window films that are applied homeowner is usually estimated to last 10-15 years.
Construction
Rooftop and attic
When the sun's shining energy attacks the roof, heating the roofing material (barrel, tile or roof sheet) and conducting roof coating, it causes the underside of the roof and roof to framing to radiate heat down through the roof space (attic/ceiling). cavity) to the attic floor/ceiling surface above. When a luminous barrier is placed between roofing material and insulation on the attic floor, most of the heat emitted from the hot roof is reflected back toward the roof and the low emissivity of the bottom of the radiation barrier means that very little heat radiation is emitted downward. This makes the upper surface of the insulation coolant larger than it should be without a luminous barrier and thereby reduces the amount of heat moving through the insulation into the space below.
This is different from the cold roof strategy that reflects the sun's energy before heating the roof, but both mean reducing radiant heat. According to a study by the Florida Solar Energy Center, white tiles or cold white metal roofs can outperform traditional black shingle roofs with a glowing barrier in the attic, but black shingle roofs with glowing barriers outperform red cooled tiles.
To install a glowing barrier under a metal roof or tile, a luminous barrier can be applied directly above the roof coating. Then the furring strip (1x4s) is applied over a luminous barrier before a metal roof or tile is applied. This feather strip ensures that a luminous barrier is facing an adequate air space. If the air space is absent or too small, heat may be able to conduct through a radiation barrier. Because the metal in the radiation barrier is highly conductive, heat transfer will be carried out by conduction and heat will not be blocked. According to the US Department of Energy, "Reflective isolation and radiation barrier products must have an air space adjacent to the reflective material to be effective."
The most common application for a luminous barrier is as facing to the attic. For traditional shingle/tile/iron roofs, a shining barrier can be applied over the rafters or frames and under the roof. This app method has a glowing barrier layer draped over a raft roll, creating a small air space above with a radiant barrier facing the entire interior attic space below. Reflective foil laminate (or sarking) is a product commonly used as a radiation barrier layer.
Another method of applying a radiation barrier to the roof in new construction is to use a laminated pre-laminated barrier to the OSB panel or roof coating. Manufacturers of this installation method often peek at labor cost savings in using products that serve as a roof decking and a glowing barrier in one.
To apply a luminous barrier in the attic, a luminous barrier may be clamped to the underside of the roof of the casing. This method offers the same benefits as the enclosed method in the double air space provided. However, ventilation should be kept open to prevent moisture trapped in the attic. In general, it is preferable to have a radiation barrier applied to the underside of the roof with a downward facing air space to prevent dust buildup, preventing the radiation barrier from carrying out.
The last method of installing a luminous barrier in the attic is to place it on top of the insulation on the attic floor. Although this method can be more effective in winter, there are some potential concerns with this application, which the US Department of Energy and the International Association for Reflective Insulation Manufacturing has felt the need to overcome. First, a breathable barrier must always be used here. This is usually achieved by small perforations on a shining barrier foil. The rate of steam transmission from a radiation barrier must be at least 5 perms, as measured by ASTM E96, and the moisture in isolation should be checked prior to installation. Second, the product must meet the required fire deployment, which includes ASTM E84 with ASTM E2599 method. Finally, this method allows the dust to accumulate above the surface of the radiation barrier, potentially reducing its efficiency over time.
Energy savings
According to a 2010 study by the Envelope Building Research Program of the Oak Ridge National Laboratory, homes with AC channels work in the attic in the hottest climate zones, such as in the US Far South, can benefit from radiation barrier interventions, with annual electricity savings up to $ 150; homes in milder climates, for example, Baltimore, can save about half of their southern neighbors. On the other hand, if there is no channel or air handler in the attic, the annual savings can be much less, from about $ 12 in Miami to $ 5 in Baltimore. However, a luminous barrier may still help improve comfort and reduce peak AC load.
Shingle temperature
One common misconception about the radiation barrier is that the heat bouncing off the glowing barrier back onto the roof has the potential to increase roof temperature and possibly damage the shingles. The performance test by the Florida Solar Energy Center showed that the temperature rise on the hottest part of the day was no more than about 5 degrees F. In fact, this study shows that a radiation barrier has the potential to lower the roof temperature after sunset. down because it prevents heat loss through the roof. RIMA International writes technical papers on subjects that include statements collected from major roof producers, and no one says that a luminous barrier will affect shingles guarantees.
Attic dust collection
When putting a radiant barrier above insulation on the attic floor, maybe dust builds up on the top. Many factors such as the size of dust particles, dust composition and the amount of ventilation in the attic affect how dust accumulates and thus the highest performance of a radiation barrier in the attic. A study by the Tennessee Valley Authority mechanically applied a small amount of dust over a shining barrier and found no significant effect when testing performance. However, TVA refers to a previous study which stated that it was possible for a radiation barrier to collect so much dust that its reflectivity could be reduced by almost half. It is not true that a two-sided glow barrier on the attic floor is immune to dust problems. The TVA study also tested a two-sided, glowing barrier with a black plastic draped over it to simulate heavy dust accumulation, as well as a single-sided side-line barrier with heavy kraft paper on it. The tests showed that the radiation barrier was not working, and the small air space created between the top of the insulation was not enough to block radiant heat.
Wall
The Radiant barrier can be used as a vented skin around the outside of the wall. Furring strips are applied to the coating to create an air space that is released between the glowing barrier and the coating, and the ventilation is used at the top and bottom to allow convective heat to rise naturally to the attic. If a brick is used on the outside, then the air space that is ventilated may already exist, and the feed strip is not required. Wrapping the house with a luminous barrier can result in a 10% to 20% reduction in tonnage air conditioning system requirements, and save on energy and construction costs.
Floor
Reflective foils, bubble foil insulation, and radiation barriers are noted for their ability to reflect unwanted solar radiation in hot climates, when applied correctly. Reflective foil made from aluminum foil with various backing such as roof paper, craft paper, plastic film, polyethylene bubble, or cardboard. Reflective bubble foils are basically bubble plastic wrap sheets with reflective foil layers and include a class of insulating products known as luminous foils. Reflective bubble/foil insulation primarily radiation barriers, and reflective insulation systems work by reducing radiant heat. To be effective, the reflective surface must face the air space, also the accumulation of dust on the reflective surface will reduce its reflective ability. A luminous barrier must be installed by minimizing the accumulation of dust on the reflective surface.
Radiation barriers are more effective in hot climates than in cold/cold climates (especially when air duct cooling is located in the attic). When the sun heats the roof, it is mainly the solar radiation energy that makes the roof become hot. Most of this heat travels through conduction through roofing material to the roof side attic. The hot roof material then emits the heat energy obtained to the cooler attic surface, including the air ducts and the attic floor. A glowing barrier reduces radiant heat transfer from under the roof to another surface in the attic. Several studies have shown that radiation barriers can reduce cooling costs by 5% to 10% when used in warm and sunny climates. Reduced heat income even allows smaller air conditioning systems. In cold climates, however, it's usually more cost-effective to install more thermal insulation than to add a luminous barrier.
Both the US Department of Energy (DOE, Energy Efficiency & Department of Renewable Energy) and the Ministry of Natural Resources (NRCAN) state that this system is not recommended for cold or very cold climates.
Canada
Canada is considered a cold climate, so these products do not work as they are promoted. Although they are often marketed as offering extremely high insulation values, there are no special standards for radiation insulation products, so beware of testimonials posted and claims of thermal performance of the manufacturer. Studies have shown that the insulation value of reflective bubble foil insulation and radiation resistance may vary from RSI 0 (R-0) to RSI 0.62 (R-3,5) per material thickness. A study conducted by CMHC (Canada Mortgage & Housing Corporation) in four homes in Paris, ON found that the performance of bubble foil is similar to an uninsulated floor. It also performs a cost-benefit analysis and the cost-benefit ratio is $ 12 to $ 13 per cubic meter RSI.
The effective insulation value depends on the amount of dead air space adjacent, the foil layer and where they are installed. If the foil is laminated to rigid foam insulation, the total isolation value is obtained by adding RSI from the foam insulation to the RSI of the dead air chamber and foil. If there is no air space or clear bubble layer, the RSI value of the film is zero.
See also
References
External links
- How the radiation barrier saves energy
- Radiant Barriers: Primary Questions and Answers
- Energy Department's Radiant Barrier Fact Sheet
- Radiant Barrier Insulation: Protection from Hot and Cold
- This entry combines public domain text from the Oak Ridge National Laboratory and the US Department of Energy. [6]
- Dept. Energy/Oak Ridge National Laboratory - Full Scale Testing Comparing Barrier Radiant Barrier, Staple Up Radiant Barrier Foil Products and Liquid Applied Low-e coating (paint radiation barrier)
Source of the article : Wikipedia
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